1. Field of the Invention
The present invention relates to a noise reduction device, a noise reduction method, and a non-transitory computer readable recording medium storing a noise reduction program that perform a noise reduction process for removing quantum noise included in a radiological image obtained by image-capturing a breast according to the amount of mammary glands included in the breast.
2. Description of the Related Art
In the related art, when performing diagnosis using a radiological image of a subject, a technique of performing image processing such as a frequency emphasis process and a gradation process with respect to a radiological image obtained by image capturing to acquire an image suitable for diagnosis and displaying the image on a display device such as a liquid crystal monitor or outputting the image as a hard-copy on a film has been used. Here, the radiological image has a problem in that quantum noise of radiation is conspicuous in a portion where the dose of radiation is small and the density is low. Thus, various methods of performing a noise reduction process for reducing or removing the quantum noise included in the radiological image as image processing with respect to the radiological image have been proposed.
As the noise reduction process, a smoothing process using a smoothing filter corresponding to quantum noise is known. For example, JP2005-021456A discloses a technique that determines the level of noise reduction using information indicating whether a portion where the degree of concentration of a density gradient vector that appears on a radiological image corresponds to a location where there is a high probability that an image of a tumor or the like is present or a location where there is a high probability that the image is noise and information indicating the dose of radiation that reaches the radiological image.